Embodiments of the present disclosure relate to fuel supply systems used for internal combustion engines.
A known fuel supply system may include a fuel pump for pressure-feeding fuel stored in a fuel tank to an internal combustion engine, a motor for driving the fuel pump, and a controller for feedback-controlling the duty ratio of the voltage applied to the motor such that the fuel pressure approaches to a target fuel pressure.
In recent years, in fuel supply systems used for vehicles, pressurized fuel supplied from a fuel piping may be injected into the engine (internal combustion engine) by injectors. In addition, in order to further improve the fuel efficiency, etc., the pressure of the fuel discharged from the fuel pump is feedback-controlled to increase or decrease the pressure of the fuel in the fuel piping according to the engine operation condition, etc.
For example, Japanese Laid-Open Patent Publication No. 2008-14183 discloses an internal combustion engine control apparatus which performs a feedback control of a fuel pump only within a predetermined range and which, if the fuel pressure is deviated from a target fuel pressure, quickly restores it to the target fuel pressure. In this internal combustion engine control apparatus, when the fuel pressure is not higher than (i.e., less than or equal to) a lower limit value of the feedback control region, the fuel pump may be driven with a maximum capability (duty ratio=100%), and when the fuel pressure is not lower than (i.e., greater than or equal to) an upper limit value of the feedback control region, the fuel pump may be stopped (duty ratio=0%) to restore it quickly to the feedback control region.
Japanese Laid-Open Patent Publication No. 2013-108503 discloses a fuel pressure control apparatus, in which the fuel pump is controlled such that the operation amount of the fuel pump is calculated from a smoothed feedback operation amount and a feed-forward operation amount in order to improve the responsiveness and convergent property during a transient period.
In the case where the feedback control of the fuel pressure is performed, if, for example, the target fuel pressure abruptly increases, there is a possibility that the rotational speed of the motor driving the fuel pump exceeds an upper limit rotational speed of the motor. If the motor is driven at a rotational speed exceeding the upper limit rotational speed, there is a possibility that the motor is stepped out, and that wear amount of bearings, etc. increases, resulting in a short service life of the motor, which is not desirable.
There has been a need in the art for techniques of inhibiting stepping-out of the motor, and for decreasing the wear amount of the bearings, etc.